Turbogenerator having rotating superconducting excitation winding



June 23, 1970 E. MASSAR 3,517,231 IURBOGENI'JHAI'OH HAVING ROTATING SUI'I'JHUONUUU'I'lNU EXCITA'I'lON WINDING .4 Slw'etS-Shee't Filed June 11, 1969 Fig.3

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E. MASSAR 3,517,231 TURBOGENERATOR HAVING ROTATING SUIERCONDUCTING June 23, 1970 EXCITATION WINDING .4 Sheets-Sheet 5 Filed June 11 1969 June23, 1970 5 MASSAR 3,517,231

'IUHHOGENURA'I'OR HAVING ROTATING SUllul C()NDUU'1.lNG

EXCITATION WINDING .4 Shea tea-Sheet 4 Filed June 11, 1969 United States Patent 3,517,231 TURBOGENERATOR HAVING ROTATING SUPER- CONDUCTING EXCITATION WINDING Ernst Massar, Erlangen, Germany, assignor to Siemens Aktiengesellschaft, a German corporation Filed June 11, 1969, Ser. No. 832,106 Claims priority, application Germany, Dec. 20, 1968, 1,815,904 Int. Cl. H02k 9/00 US. Cl. 31052 24 Claims ABSTRACT OF THE DISCLOSURE The rotary excitation winding of a turbogenerator is affixed to the surface of a carrier cylinder which faces the core of the rotor. The carrier cylinder and excitation winding are spaced from the core to form a vacuum chamber therebetween. The cylinder is affixed to the core by a plurality of holding members of poor thermal conductivity. The excitation winding has conductors of high field superconducting material and conductors of normal conducting material having good electrical conductivity properties at operating temperatures. The normal conducting conducters are arranged so that alternating currents which occur in the excitation winding during the operation of the turbogenerator occur only in such conductors. Coolant ducts extend substantially parallel to and are connected to the normal conducting conductors.

DESCRIPTION OF THE INVENTION The present invention relates to a turbogenerator. More particularly, the invention relates to a turbogenerator having a rotating superconducting excitation winding.

A turbogenerator with a rotating superconducting excitation winding is disclosed in Austrian Pat. 258,404. The turbogenerator of the Austrian patent has a multilayer winding comprising a superconducting conductor and being positioned in a carrier body which encloses the winding. The carrier body is positioned in a slot bar which is tightly wedged into the rotor of the turbogenerator. The winding is supported by tensioning or tie bars. The carrier body is thermally insulated from the slot bar and is cooled in order to cool the Winding.

The turbogenerator of the type disclosed in the Austrian patent creates difiiculties when the generator is utilized to provide very high output power. This is due to the fact that the operation of the generator, during nonstationary phenomena such as short-circuits or strong load fluctuations, may induce alternating fields and alternating currents in the excitation winding. These induced fields and currents may result in alternating current losses in the superconducting material of the winding, thereby heating said winding. Under adverse circumstances, the heating of the winding may result in a transition of said winding from a superconducting condition to a normal conducting condition, unless the heat is dissipated, while it is developing, in sufficient time to prevent a transition from the superconducting to the normal conducting condition. Since the winding of the known turbogenerator comprises a multilayer wire and the carrier body must be simultaneously cooled, an increase in the output power will result in an increase in the required cooling power and in the amount of and expense for coolant.

The principal object of the present invention is to provide a new and improved turbogenerator.

An object of the present invention is to provide a turbogenerator having a rotating superconducting excitation winding, which turbogenerator overcomes the disadvanta-ges of known turbogenerators of similar type.

An object of the present invention is to provide a turbo- Patented June 23, 1970 generator having a rotating superconducting excitation winding, in which alternating current losses in the excitation winding are minimized.

An object of the present invention is to provide a turbogenerator having a rotating superconducting excitation winding, which turbogenerator functions at maximum efficiency, effectiveness and reliability.

In accordance with the present invention, a turbogenerator comprises a rotor having a core. A carrier cylinder of non-magnetic material encloses the core. A plurality of holding members of poor thermal conductivity aflix the carrier cylinder to the core. A rotary excitation winding is affixed to the carrier cylinder on a surface of the carrier cylinder facing the core. The carrier cylinder and excitation winding are spaced from the core to form a vacuum chamber therebetween. The vacuum chamber provides thermal insulation. The holding members extend through the vacuum chamber. The excitation winding has conductors of high field superconducting material and conductors of normal conducting material having good electrical conductivity properties at operating temperatures. The normal conducting conductors are arranged so that alternating currents which occur in the excitation winding during the operation of the turbogenerator occur only in the normal conducting conductors. Coolant ducts extend substantially parallel to and are connected to the normal conducting conductors.

The excitation winding and the coolant ducts are combined into a single excitation winding coolant duct unit. The excitation winding coolant duct unit may comprise a tube of normal conducting material having a substantially rectangular cross-section formed by substantially planar inner surfaces. A band of normal conducting material is affixed to and extends along one of the inner surfaces of the tube and has a plurality of conductors of high field superconducting material embedded therein and extending therewith. The conductors of high field superconducting material comprise superconducting wires parallel to and spaced from each other.

The excitation winding coolant duct unit may comprise two tubes of normal conducting material each having substantially rectangular cross-section. The tubes are spaced from each other by a small distance. A band of normal conducting material is positioned between and extends along the tubes and has a plurality of conductorsof high field superconducting material embedded therein and extending therewith.

The excitation winding coolant duct unit may comprise a tube of normal conducting material having a substantially rectangular cross-section having a plurality of conductors of high field superconducting material embedded therein and extending therewith. The tube has a plurality of substantially planar inner surfaces forming its rectangular cross-section and a plurality of substantially planar outer surfaces substantially parallel to the inner surfaces. The conductors of high field superconducting material comprise superconducting wires spaced from each other and spaced from each of the outer surfaces substantially parallel to the axis of the core by a distance greater than five times the depth at which AC components penetrate the tube of normal conducting material. The distance is greater than 2.5 mm.

The excitation winding coolant duct unit may comprise a tube of electrical insulating material having a substantially rectangular cross-section formed by substantially planar inner surfaces. Each of two bands of normal conducting material is provided on one of the inner surfaces opposite the other and extends therealong. A third band of normal conducting material extends substantially radially to the core and between and substantially perpendicular to the two bands of normal conducting material. The

third band of normal conducting material extends with the two bands of normal conducting material and forms therewith an I in cross-section and thereby divides the tube in half along its length to form two independent ducts. The third band has a plurality of conductors of high field superconducting material embedded therein and extending therewith.

The carrier cylinder may comprise non-magnetic steel insulated from the exictation winding. The carrier cylinder may also comprise fiber-reinforced synthetic material. A damping cylinder of non-magnetic normal conducting material may be affixed to the core and surrounds the carrier cylinder.

The carrier cylinder is mounted on the core by axial mounting means. The axial mounting means may comprise a support member of hollow substantially cylindrical configuration of poor thermal conductivity having one base area afiixed to the carrier cylinder in the area of one base of the carrier cylinder and another base area aflixed to the core. The support member of the axial mounting means may be of hollow substantially frustoconical configuration and may have a plurality of holes formed therethrough.

The core has a plurality of spaced planar surfaces formed on its peripheral surface in different areas. The carrier cylinder is atfixed to the core by torque transfer means which transfers torque from the core to the carrier cylinder. The torque transfer means comprises support strips of poor thermal conductivity extending substantially parallel to the planar surfaces formed on the core. Each of the support strips has one end affixed to the carrier cylinder and another end affixed to the core. Each of the support strips of the torque transfer means may be afiixed to the core by fibers of material of poor thermal conductivity. Each of the support strips of the torque transfer means may have ribs formed therein and extending along its length. The core may have a plurality of spaced bores forme dtherein extending radially inwardly from its peripheral surface. The carrier cylinder is affixed to the core by fastening means. The fastening means comprises support rods of poor thermal conductivity housed in the bores formed in the core. Each of the support rods has one end aflixed to the carrier cylinder and another end afiixed to the core at the base of a corresponding one of the bores.

A rotor shaft extends from one end of the core and has an axis. Coolant supply means supplies coolant to the excitation winding coolant duct unit. The coolant supply means may comprise a tubular supply duct coaxial with the axis of the rotor shaft extending in axial direction from one end of the rotor shaft into the core and through the core to the excitation Winding coolant duct unit. Coolant removal means removes coolant from the excitation winding coolant duct unit. The coolant re moval means may comprise another tubular duct coaxially surrounding the supply duct and extending from the excitation Winding coolant duct unit through the core to the rotor shaft and through the rotor shaft to one end of the rotor shaft. Thermal insulating means is provided around the coolant supply means and the coolant removal means for insulating the coolant supply means and the coolant removal means from each other, from the rotor shaft and fIOIIll the core. The thermal insulating means comprises a vacuum chamber.

Two thermally insulated normal conducting rings may coaxially surround the rotor shaft at one end thereof. Each of the rings has a substantially cylindrical outer peripheral surface and a substantially cylindrical inner surface. Each of a pair of normal conducting current leads electrically contacts the peripheral surface of a corresponding one of the rings. Each of a pair of conductors comprising normal conducting material and high field superconducting material electrically contacts the inner surface of a corresponding one of the rings in radial alignment with the point of contact of the corresponding normal conducting current lead. A thermally insulated bore is formed in the rotor shaft and extends to the tubular supply duct of the coolant supply means. A thermally insulated bore is formed in the rotor shaft and extends to the other tubular duct of the coolant removal means. One of the pair of conductors extends through one of the bores and the tubular supply duct to the excitation winding coolant duct unit. The other of the pair of conductors extends through the other of the bores and the other tubular duct to the excitation winding coolant duct unit. The coolant from the coolant removal means cools the rings and parts of the pair of conductors.

In order that the present invention may be readily carried into effect, it will now be described with reference to the accompanying drawings, wherein:

FIG. 1 is a longitudinal sectional view of part of the rotor and stator of an embodiment of the turbogenerator of the present invention;

FIG. 2a is a sectional view of the excitation winding coolant duct unit of the turbogenerator of the present invention, illustrating the stray magnetic field lines during the occurrence of AC components therein;

FIG. 2b is a schematic diagram of part of the excitation winding coolant duct unit of the turbogenerator of the present invention, illustrating the stray magnetic cfield lines and the alternating current during the occurrence of alternating current therein;

FIG. 3 is a sectional view of an embodiment of the excitation winding coolant duct unit of the turbogenerator of the present invention;

FIG. 4 is a sectional view of another embodiment of the excitation winding coolant duct unit of the turbogenerator of the present invention;

FIG. 5 is a sectional view of another embodiment of the excitation winding coolant duct unit of the turbogenerator of the present invention;

FIG. 6 is a sectional view of another embodiment of the excitation winding coolant duct unit of the turbogenerator of the present invention;

FIG. 7 is a longitudinal sectional view of part of the rotor and stator of another embodiment of the turbogenerator of the present invention;

FIG. 8 is a cross-sectional view through part of 'an embodiment of the turbogenerator of the present invention;

FIG. '9 is a sectional view of part of FIG. 8, on an enlarged scale;

FIG. 10a is a sectional view of another embodiment of the holding strip of FIG. 9;

FIG. 10b is a sectional view taken along the lines XX of FIG. 10a;

FIG. 11 is a longitinal sectional view of part of the turbogenerator of the present invention illustrating the coolant supply and coolant removal duct system; and

FIG. 12 is a cross-sectional view taken along the lines XIIXII of FIG. 11.

In FIG. 1, the stator 1 includes a water-cooled stator winding of normal conducting material. A rotor 2 is provided in operative proximity with the stator 1. The rotor excitation winding comprises superconducting material and normal conducting material having end turns 3. The longitudinal portions 4 of the excitation winding extend substantially parallel to the axis 2 of the rotor 2.

The excitation Winding is aflixed to a carrier cylinder 6 comprising fiber-reinforced synthetic material. The excitation winding is affixed to a surface of the carrier cylinder 6 facing the core 5 of the rotor 2. The carrier cylinder relieves the excitation winding from centrifugal forces occurring during the rotation of the rotor. The carrier cylinder 6 is aflixed in axial direction by an axial mounting device which mounts said carrier cylinder on the core 5. The axial mounting device comprises a support member 7 of hollow substantially cylindrical configuration. The configuration of the support member 7 is actually frustoconical.

The support member 7 encloses the core 5 and comprises material of poor thermal conductivity having one base area aflixed to the carrier cylinder 6 in the area of one base of said carrier cylinder and another base area affixed to the core 5.

A ring 8 is utilized toaffix the smaller diameter end of the support member 7 to the core 5. A ring 9 is utilized to affix the larger diameter end of the support member 7 to the carrier cylinder 6. The support member 7 may, of course, be affixed to each of the carrier cylinder 6 and the core 5 by any suitable means such as, for example, bolts, rivets, or the like. A support member, identical with the support member 7, is utilized at the other end (not shown) of the turbogenerator to affix the carrier cylinder 6 to the core 5.

A damping cylinder 10 of non-magnetic normal conducting material surrounds the carrier cylinder 6 and is affixed to the core 5- via steel members 11 and 12 of substantially ring configuration. The damping cylinder 10 comprises non-magnetic steel. The ring members 11 and 12 may be affixed to the damping cylinder 10 by any suitable means such as, for example, bolts 13. The damping cylinder 10 and the ring members 11 and 12 form the outer housing or outer wall of a vacuum chamber 14 which provides thermal insulation between the excitation winding 3, 4, the carrier cylinder 6 and the other components of the turbogenerator. Since the damping cylinder 10 and the ring members 11 and 12 form such outer housing, the areas of abutment of said ring members are provided with sealing rings 15. The sealing rings 15, comprise an appropriate metal. The vacuum 14 may have a pressure of 10- torr, for example.

Each of the conductors of the excitation winding 3, 4 comprises a duct 16 through which coolant is pumped during the operation of the turbogenerator. The coolant cools the excitation winding and the carrier cylinder 6 to a low temperature. The core 5, the damping cylinder 10 and the ring members 11 and 12 do not require cooling, and are maintained at room temperature. To maintain the heat absorption into the vacuum chamber 14 as low as possible, the surfaces of the core 5, the damping cylinder 10 and the ring supports 11 and 12 which face each other may be polished to a high gloss or may be provided with a layer of reflective material.

The individual turns of the excitation winding may be provided with layers of electrical insulating material therebetween (not shown in FIG. 1), or may be spaced a sufficient distance from each other so that the spaces between said turns function as insulation. In order to prevent the turns of the excitation winding from shifting due to torque during operation of the turbogenerator, grooves 17 may be formed in the surface of the carrier cylinder 6. The grooves may follow the pattern of the excitation winding and said excitation winding is seated or arranged in said grooves. The turns of the excitation winding may be afiixed to the carrier cylinder 6 by any suitable means such as, for example, bolts.

As indicated in FIG. 2a, when an alternating current is induced in the excitation winding 4, it produces a magnetic flux In FIG. 2b, the instantaneous magnitudes of the alternating current are indicated as xs in two component conductors 20 and 21 of the excitation winding. Each x represents an equal magnitude of alternating current. A plurality of magnetic lines of force 23, produced by the alternating current, are shown in FIG. 2b. The direct current flowing through the excitation winding and the magnetic lines of force produced by said direct current, are not shown in FIG. 2b.

As indicated in FIG. 2b, there is, primarily, a bilateral current displacement of the alternating currents or AC components. That is, the displacement is toward the outer surfaces 24 of each of the conductors 20 and 21 which face the carrier cylinder 6 (not shown in FIG. 2b) and toward the outer surfaces 25 of said conductors which face the core 5 (not shown in FIG. 2b). The AC components therefore flow essentially on the surface of the conductors of the excitation winding. At the low temperatures utilized to cool the excitation winding, of approximately 4 to 5 K., the depth of penetration of the AC components into the conductors is approximately 0.5 mm. The depth of penetration is defined as the distance from the surface of the conductor at which the alternating current decreases to l/e of its magnitude at said surface.

To insure that the superconducting conductors of the conductors of the excitation Winding are maintained free from the AC components, the distance of said superconducting conductors from the surfaces 24 and 25 of said conductors should be greater than five times the depth of penetration. The superconducting conductors of each conductor of the excitation winding should thus be more than 2.5 mm. from each of the surfaces 24 and 25.

It may be of advantage to provide the superconducting conductors at a distance from the surfaces 24 and 25 even greater than ten times the depth of penetration. Such distance is greater than about 5 mm.

FIG. 2a illustrates an arrangement or device for afiixing the excitation winding to the carrier cylinder 6. The turns of the winding are passed through a plate 26 of electrical insulation material. The plate 26 is bolted to the carrier cylinder 6 by bolts 27. The turns of the excitation winding are seated in grooves 17 formed in the surface of the carrier cylinder 6. Additional electrical insulation material (not shown in FIG. 2a) may be provided between the bolts 27 and the turns 4 of the excita tion winding.

FIGS. 3, 4, 5 and 6 illustrate different embodiments of a conductor of the excitation winding of the turbogenerator of the present invention. Each of the conductors of FIGS. 3, 4, 5 and 6, is combined with any coolant duct into a single excitation winding coolant duct unit.

In the embodiment of FIG. 3, the excitation winding coolant duct unit comprises a tube 31 of normal conducting material having a substantially rectangular crosssection formed by substantially planar inner surfaces. A band 34 of normal conducting material is affixed to and extends along one of the inner surfaces of the tube 31. The band 34 of normal conducting material has a plurality of conductors 33 of high field superconducting material embedded therein and extending therewith. The

superconducting conductors or wires 33 extend substantially parallel to each other.

A particularly suitable normal conducting material is copper. The superconducting conductors may comprise, for example, niobium-zircon or niobium-titanium. The normal conducting band 34 may be aflixed to the tube 31 by'any suitable means such as, for example, welding, soldering, or the like. The tube 31 may comprise two parts, for example, which may, for example, be welded or soldered to each other at the areas 35 and 35', for example.

When AC components occur, due tostrong load pulses or a short-circuit, such components flow almost completely in regions 36 and 37 adjacent the outer surfaces of the tube 31 which face the carrier cylinder 6 and the core 5, respectively. On the other hand, direct current flows in the superconducting conductors or wires 33. Due to the relatively large surface of the tube 31 and particularly due to the width of the regions or areas 36 and 37, the alternating current prevails over a large cross-section, so that thelosses in alternating current remain relatively slight. Furthermore, the developing dissipated heat may be readily transferred through the walls of the tube 31 to the coolant flowing through the cavity or duct 38 formed in the center of said tube, since said walls have good thermal or heat conductivity.

The excitation winding coolant duct unit of FIG. 4 comprises two tubes 41 and 42 of normal conducting material each having a substantially rectangular crosssection. The tubes 41 and 42 are spaced from each other by a small distance. Coolant flows through the ducts formed by the tubes 41 and 42. A band 43 of normal conducting material is positioned between and extends along the tubes 41 and 42 and has a plurality of condoctors 44 of high field superconducting material embedded therein and extending therewith. The band 43 is aflixed to the tubes 41 and 42 by any suitable means such as, for example, welding or soldering, and is in good electrical contact with said tubes.

The excitation winding coolant duct unit of FIG. comprises a tube 51 of normal conducting material having a substantially rectangular cross-section. A plurality of conductors 52 of high field superconducting material are embedded in the tube 51 and extend therewith. The excitation winding coolant duct unit of FIG. 5 may be produced, for example, by extrusion or by cold drawing or rolling. Copper is preferred as the normal conducting material. Aluminum is also preferred.

The tube 51 has a plurality of substantially planar inner surfaces forming its rectangular cross-section and a plurality of substantially planar outer surfaces, including the surfaces 53 and 54, substantially parallel to the inner surfaces. The conductors 52 of high field superconducting material are spaced from each other and spaced from each of the outer surfaces 53 and 54 which are substantially parallel to the axis of the core 5 (not shown in FIG. 5), by a distance greater than five times the depth to which AC components penetrate the tube 51.

In FIG. 6, the excitation winding coolant duct unit comprises a tube 65 of electrical insulating material having a substantially rectangular cross-section formed by substantially planar inner surfaces. A band 63 of normal conducting material is positioned on one of the inner surfaces opposite the other and extends therealong. A band 64 of normal conducting material is positioned on the other of the inner surfaces opposite the one and extends therealong. A third band 61 of normal conducting material extends substantially radially to the core 5 (not shown in FIG. 6) and between and substantially perpendicular to the two bands 63 and 64 of normal conducting material.

The third band 61 extends with the two bands 63 and 64 of normal conducting material and forms therewith an I or H lying on its side in cross-section, thereby dividing the tube 65 in half along its length to form two independent ducts 66 and 67. A plurality of conductors 62 of high field superconducting material are embedded in the band 61 and extend therewith.

The coolant flows through the separate cavities or ducts 66 and 67. The AC components flow through the normal conducting bands 63 and 64. The tube 65 may comprise any suitable synthetic material and may be pressed around the bands 61, 63, and 64 in an extrusion process. Additional insulation is not required for the excitation winding coolant duct unit of the embodiment of FIG. 6.

FIG. 7 illustrates another part of another embodiment of the turbogenerator of the present invention. The excitation winding 71, 72 is the same as that of the embodiment of FIG. 1 and is positioned in the same manner. The excitation winding 71, 72 is afiixed to a carrier cylinder 74 which is similar to the carrier cylinder 6 of FIG. 1 and is positioned on the surface of said carrier cylinder facing the core 73 of the rotor of the turbogenerator. A layer 75 of electrical insulating material is provided be tween the excitation winding 71, 72 and the carrier cylinder 74 and insulates said winding from said carrier cylinder, which comprises nonmagnetic steel.

The carrier cylinder 74 is affixed to the core 73 and is fixed in axial direction by a support member 76. The support member 76 functions in the same manner as the support member 7 of the embodiment of FIG. 1. The support member 76 is of cylindrical configuration and surrounds the rotor 73. The support member 76 may comprise a fiber-reinforced synthetic material.

The support member 76 has a plurality of holes 77 formed therethrough. The holes 77 function to reduce the cross-section available for thermal conductance. One end of the support member 76 is aifixed to the core 73 by any suitable means, and the other end of said support member is aflixed to a ring 78 of the carrier cylinder 74. A damping cylinder 79, which is similar to the damping cylinder 10 of the embodiment of FIG. 1, encloses the carrier cylinder 74. The damping cylinder 79 is alfixed t0 the core 73 via a steel ring type member 80.

The points of contact or abutment between the damping cylinder 79 and the ring-shaped steel part 80, and between said steel part and the core 73, are sealed by sealing rings 81. A space 82 is formed between the damping cylinder 79 and the core 73. The carrier cylinder 74 is positioned in the space 82, as is the excitation winding coolant duct unit 71, 72. The space 82 is evacuated during operation of the generator.

FIG. 8 is a cross-section through the rotor, illustrating ing a torque transfer device or arrangement for transferring torque from the core 91 to the carrier cylinder 93. The cross-section of FIG. 8 is actually three cross-sections, taken at three different points on the axis of the rotor. The torque, or more particularly, the forces produced by the torque, is or are transferred from the core 91 to the carrier cylinder 93 by a plurality of support strips 94.

A plurality of spaced planar surfaces are formed on the peripheral surface of the core 91 in different areas thereof. The support strips 94 are of poor thermal conductivity and extend substantially parallel to the planar surfaces formed on the core 91. The support strips 94 may be positioned at any number of place along the rotor axis, and are preferably positioned at four equidistant positions on the periphery of the core 91, so that the carrier cylinder 93 is supported by a four point suspension. The support strips may comprise a fiber-reinforced synthetic material.

One end of each of the support strips 94 is aflixed to the carrier cylinder 93 and the other end of each of said support strips is afiixed to the core 91. The planar surfaces formed in the peripheral surface of the core 91 are substantially tangential to said core, so that the support strips 94 extend substantially tangentially to said core. The support strips 94 may be aflixed to the carrier cylinder 93 by any suitable means such as, for example, clamps 96 fastened by bolts 95. The expansion of the support strips 94 in a direction parallel to the axis of the rotor may be greater than the distance between the point at which said support strips are affixed to the carrier cylinder 93 and the carrier 91. Each pair of support strips 94 is then in angular disposition. The angle between the support strips 94 of each pair thereof is obtuse.

A plurality of spaced bores 99 and are formed in the core 91 extending radially towardly from the peripheral surface of said core. A fastening device or arrangement afiixes the carrier cylinder 93 to the core 91 and comprises support rods 97 and 98, as shown in FIG. 8. The support rods 97 and 98 may be of cylindrical configuration and comprise fiber-reinforced synthetic material of poor thermal conductivity.

The support rods 97 and 98 are housed or arranged in the bores 99 and 100 of the core 91. Each support rod has one end aflixed to the carrier cylinder 93 and the other end aflixed to the core 91 at the base of the corresponding one of the bores. The support rods 97 and 98 may be affixed to the carrier cylinder 93 by any suitable means such as, for example, bolts 101. The bores 99 and 100 are provided at various positions along the axis of the rotor and at preferably four equidistant positions around the circumference of the core 91. The positions of the bores along the axis of the rotor may be those of the support strips 94 or may be where said support strips are not positioned.

The bores 99 and 100 open into the vacuum chamber provided between the core 91 and the carrier cylinder 93, in which vacuum chamber the excitation winding coolant duct unit 92 is positioned. The inside surfaces of the bores 99 and 100 may be provided with reflecting material or may be polished to a high gloss in order to reduce heat absorption. If possible, the surfaces of the support rods or cylinders 97 and 98 should be provided with reflective material or polished to a high gloss to further reduce heat absorption.

FIG. 9 illustrates a preferred arrangement or device for affixing the support strips 94 to the core 91. In FIG. 9, a steel bar 111 is affixed to the core 91 at a planar surface 110 thereof. The steel bar 111 is aifixed to the core 91 by any suitable means such as, for example, bolts. One end of the support strip 94 is affixed to the bar 111 by a support or holding member 112 and bolts 113. To prevent deformation of the support strip 94 by centrifugal forces which occur during the operation of the turbogenerator, the support strip 94 is wired to the bar 111, and is therefore wired to the core 91. The support strip 94 is wired to the bar 111 by fibers of material of poor thermal conductivity such as, for example, nylon threads 115. The nylon threads 115 extend through bores 114 formed through the support strip 94 and bores formed through the bar 111.

FIG. a is a cross-sectional view through part of the rotor 91, illustrating another device or arrangement for affixing a support strip '117 to said core. The support strip 117 may comprise, for example, fiber-reinforced synthetic material. The support strip 117 has ribs 116 formed therein and extending along its length in the area of the planar surface provided on the peripheral surface of the core 91 for said support strip. The end of the support strip .117 at the core 91 is afiixed to said core by support or holding members 118 and 119 and bolts .140. The other end of the support strip 117 (not shown in FIG. 10a) is affixed to the carrier cylinder 93 (not shown in FIG. 10a) in the manner illustrated in FIG. 8.

The planar surface provided on the peripheral surface of the core 91 has a plurality of grooves 141 formed therein. The grooves 141 correspond with the ribs 116 of the support strip 117, so that said ribs are housed or arranged in said grooves. A cross-sectional view of the support strip 117 and the corresponding grooved planar surface of the core 91 is illustrated in FIG. 10b. The ribs 116 of the support strip 117 extend in spaced parallel relationship with each other as do the grooves 141 of the planar surface of the core 91.

FIGS. 11 and 12 illustrate a preferred embodiment of a coolant duct arrangement and an electrical conductor arrangement of the turbogenerator of the present invention. The individual components of the rotor have the same reference numerals as the corresponding components shown in FIG. 7. A rotor shaft 121 extends from one end of the core 73 and has an axis which is coincident with the axis of said core.

A coolant supply system supplies coolant to the excitation winding coolant duct unit 71. The coolant supply system comprises a tubular supply duct 120 coaxial with and surrounding the axis of the rotor shaft 121 and extending in axial direction from one end of said rotor shaft into the core 73 and through said core to the excitation winding coolant duct unit 71. A coolant removal system removes coolant from the excitation winding coolant duct unit. The coolant removal system comprises another tubular duct 122.

The tubular duct 122 coaxially surrounds the supply duct 120 and extends from the excitation winding coolant duct unit 71 through the core 73 to the rotor shaft .121 and through said rotor shaft to the one end of said rotor shaft. Thermal insulation, in the form of a vacuum chamber 123, is provided around the ducts to insulate the coolant supply duct 120* from the coolant removal ducts 121 and to insulate said ducts from the rotor shaft 121 and the core 73.

Current is supplied to the excitation winding coolant duct unit 71 by a current supply system. The current supply system comprises two thermally insulated normal conducting rings 124 and 125 coaxially surrounding the rotor shaft 121 at the one end thereof. Each of the rings 124 and 125 comprises, for example, copper. The rings 124 and 125 rotate with the rotor shaft 121. Each of the rings 124 and 125 has a substantially cylindrical outer peripheral surface and a substantially cylindrical inner surface.

A normally conducting current lead 126 electrically contacts the outer peripheral surface of the ring 124. A normal conducting current lead 127 electrically contacts the outer peripheral surface of the ring 125. A conductor 128 comprising normal conducting material and high field superconducting material electrically contacts the inner surface of the ring 124 in radial alignment with the point of contact of the corresponding normal conducting current lead 126. A conductor .129 comprising normal conducting material and high field superconducting material electrically contact the inner surface of the ring 125 in radial alignment with the point of contact of the corresponding normal conducting current lead 127.

The normal conducting current leads 126 and 127 extend along the rotor shaft 121 and are insulated from said rotor shaft. The normal conducting current leads are connected to rotating rectifiers (not shown in FIGS. 11 and 12).

A thermally insulated bore 130 is formed in the rotor shaft 121 and extends to the tubular supply duct of the coolant supply system. A thermally insulated bore 131 is formed in the rotor shaft 121 and extends to the other tubular duct 122 of the coolant removal system. The conductor 128 of normal conducting and superconducting material extends through the bore 130 and the tubular supply duct 120' to the excitation winding coolant duct unit 71. The other conductor 129 of normal conducting and superconducting material extends through the bore 131 and the other tubular duct 122 to the excitation winding coolant duct unit 71. The rings 124 and may be affixed by support members of poor thermal conductivity such as, for example, nylon threads, within a vacuum chamber 132.

Coolant is supplied to the coolant supply duct 120 at the one end of the rotor shaft 121 and flows through said duct, cooling the current conductor 128. After passing through and cooling the excitation winding coolant duct unit 71, the coolant is removed from said unit via the coolant removal duct 122 and cools the current conductor 129. Part of the coolant continues to flow through the coolant removal duct 122 to the end of the rotor shaft .121, Where it is removed from the rotor. Another part of the coolant, which flows through the excitation winding coolant duct unit 71, also flows through the bores 130 and 131 formed through the rotor shaft 121 and cools the current conductors 128 and 129 extending through said bores. The coolant flows toward the rings 124 and 125 and cools said rings as well as the current conductors 128 and 129.

The coolant then flows around the rotor shaft 121 and is removed from the turbogenerator via an outlet 133 provided in the vacuum chamber 132 which surrounds the rings 124 and 125. The outlet 133 opens into a stationary housing 134 for the rings 124 and 125. The stationary housing 134 encloses the vacuum chamber 132. The coolant flowing through the outlet 133 is supplied to a coolant recovery unit via a duct or pipe 136 affixed to the stationary housing 134 by a suitable coupling 135. The stationary housing 134 is sealed from the rotating rotor shaft 121 by labyrinth seals 137.

The coolant may comprise any suitable coolant fluid. A coolant which is preferably utilized is supercritical gaseous helium, which is helium having a temperature greater than 5.2 K. and a pressure greater than 2.25

atmospheres. In order to insure that the cooling cycle remains reliable despite the great centrifugal forces which occur during the rotation of the rotor, the supercritical helium is preferably pumped through the excitation winding coolant duct unit. The pump may be provided at the end of the coolant removal duct 122 and the coolant removal pipe 136. The pump output of the pump may be adjusted to distribute the coolant flowing through the ducts in a manner whereby the current conductors 128 and 129 and the rings 124 and 125 are satisfactorily cooled.

Since the coolant absorbs heat in the excitation winding coolant duct unit 71, the coolant which is removed from said unit has a higher temperature than the coolant which is supplied to said unit. It is thus preferable to utilize a superconducting material having a high critical temperature in the current conductors 128 and 129. A suitable superconducting material, having a high critical temperature, may comprise, for example, an intermetallic compound Nb Sn, the critical temperature of which is about 18 K. The normal conducting material of the current conductors 128 and 129 is preferably copper, since copper enhances the electrical stability of the super conducting material.

The turbogenerator of the present invention is particularly suitable for producing high outputs. The peak output power of known two pole turbogenerators, having a water cooled normal conducting excitation winding and an active iron length of approximately 8 m., is approximately 1200 mva., due to sharply increasing losses. The turbogenerator of the present invention may provide an output power of approximately 2000 mva. and more, when it is of the same dimensions as the known turbogenerators. The turbogenerator of the present invention permits an increase of the inductance by at least 25% and the ampere-turns per cm. by at least 35% to 40% in relation to the known turbogenerators, While excitation losses are reduced to a fraction of those suifered in normal conducting windings.

The cooperation of the various components of the turbogenerator of the present invention results in high operating safety for said turbogenerator. Since the conductors of the excitation winding include high field superconducting material such as, for example, niobiumzirconium, niobium-titanium or Nb Sn, said conductors have very high critical magnetic fields and critical currents. That is, they pass from a superconducting to a normal conducting condition in very high magnetic fields, or when charged with very high currents. Since the currents and fields which occur during normal operation of the turbogenerator are considerably less than such critical values, said turbogenerator is able to Withstand considerable overloading without causing the winding to pass from a superconducting to a normal conducting condition. If the excitation winding should pass from a superconducting to a normal conducting condition, however, due to an operational disturbance or an operating fault, the current flowing through said winding would be absorbed partially or completely by the normal conducting material such as, for example, copper or aluminum, without causing an inadmissible increase in the magnitude of the conductor temperature. Such an increase in the conductor temperature could damage or destroy the excitation winding. The normal conducting material thus functions to provide electrical stabilization.

The cross-section of the normal conducting material of the conductor should usually be large relative to the cross-section of the high field superconducting material. The special arrangement of the normal conducting material insures that the alternating currents induced in the excitation winding, having frequencies of 50 or 100 Hertz or more, do not flow through the superconducting material of said winding. Thus, substantially no alternating current losses occur in the superconducting material. The metal connection, of good thermal conductivity, of the conductor of the excitation winding with the coolant duct provides satisfactory cooling of said winding and an intermediate removal of dissipated heat which may occur in such conductor. When the conductor of the excitation winding itself functions simultaneously as a duct for the coolant, cooling is further improved, and the cross-section utilized for the duct of the coolant may be utilized to provide electrical stabilization.

The positioning of the excitation winding on the inner surface of the carrier cylinder and its insulation, with said carrier cylinder, from the adjacent components by means of a vacuum chamber, and the aflixing of the carrier cylinder to the core by support members having poor thermal conductivity, provide several advantages. The excitation winding is completely relieved of the effect from centrifugal forces. The forces produced by the torque may be transferred to the carrier cylinder without appreciable impairment of the heat insulation of the excitation winding. Since only the carrier cylinder and the excitation winding must be cooled, a relatively small area must be cooled.

Since the carrier cylinder is aflixed to the core by support members, which extend through the vacuum chamber and which have poor thermal conductivity, there is very little heat transferred from the core to the carrier cylinder and the excitation winding. Furthermore, the advantageous cooling effect is enhanced and is due to the combination of the excitation winding and the coolant duct into a single excitation winding coolant duct unit. Since the carrier cylinder comprises non-magnetic material, the magnetic field produced by the excitation winding is substantially undistorted by the carrier cylinder.

The embodiment of FIG. 4 of the excitation winding coolant duct unit is preferable when a particularly large cross-section of the normal conducting material is necessary to provide for electrical stabilization. The embodiment of FIG. 4 also provides particularly intensive cooling, due to the provision of two coolant ducts. The bands utilized in the various embodiments of FIGS. 3, 4, 5 and 6 having high field super-conducting conductors embedded therein, may be prefabricated, if necessary or desired. The high field superconducting material embedded in the nor-mal conducting material of the band preferably comprises superconducting conductors or wires spaced from and parallel to each other. In such an arrangement, a superconducting conductor may be bypassed by others of the superconducting conductors, when there is overloadmg.

The copper or aluminum utilized for the normal conducting material is preferably of the highest possible purity, of greater than 99.999% by weight. This permits the greatest possible electrical conductivity at low operating temperatures of approximately 4 to 5 K., and results in a reduction of the alternating current losses in the normal conducting material.

The carrier cylinder may comprise a fiber-reinforced synthetic material such as, for example, epoxy resin having glass fibers or spun glass insertions. This prevents eddy current losses caused by alternating current components from occurring in the carrier cylinder. The damping cylinder functions to keep the alternating current components away from the normal conducting material for the excitation coil, as much as possible, thereby reducing the alternating current losses.

The support members 7 and 76 preferably comprise fiber-reinforced synthetic material. Each of the support members extends, between the points at which it is afiixed to the core and to the carrier cylinder, for approximately one third the core length of the rotor, or more. Due to the length of the support member 7 and 76 between the points at which it is aflixed to the carrier cylinder and the core, the influx of heat from the core to the cooled carrier cylinder is maintained at a minimum. An additional extension of the thermal path and a further reduction of the heat conducting cross-section of the support members 7 and 76 is provided by the holes formed through the support member 76. Such holes may be formed through the support member 7, if desired.

The support strips 94 are relatively long, so that the heat which flows from the core to the carrier cylinder via said support strips must travel a long distance. The nylon threads or the ribs and corresponding grooves prevent deformation of the support strips by centrifugal force during operation of the turbogenerator. The support rods 97 and 98 also provide long thermal paths between the carrier cylinder and the core.

The coolant may comprise liquid helium, or any other suitable coolant, as an alternative to supercritical gaseous helium. Any pumps which may be utilized, for circulating the coolant or other purposes, are preferably positioned outside the turbogenerator. The end of the rotor shaft is preferably provided with labyrinth seals to connect the circulating coolant supply ducts in the rotor shaft with the stationary supply ducts from the source of coolant. The turbogenerator is preferably excited via rotating rectifiers in a system described in an article by Heinrichs and Abolins on pages 1 to 8 of Elektrotechnische Zeitschrift, issue 9, vol. 87, 1966.

In order to provide economic consumption of coolant and reliable operational safety of the turbogenerator, the excitation current should be supplied to the excitation winding in a manner whereby the introduction of heat to the superconducting winding and ohmic losses in the ducts and conductors is maintained as low as possible. The rings 124 and 125 assist in providing a relatively long cooling path between the current conductors of normal conducting material from the rotating rectifiers and the conductors extending into the rotor. The heat transferred from the normal conducting current conductors to the conductors passing through the rotor may thus be maintained relatively low.

While the invention has been described by means of specific examples and in specific embodiments, I do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

I claim:

1. A turbogenerator, comprising a rotor having a core;

a carrier cylinder of non-magnetic material enclosing said core;

a plurality of holding members of poor thermal conductivity aflixing said carrier cylinder to said core;

a rotary excitation winding affixed to said carrier cylinder on a surface of said carrier cylinder facing said core, said carrier cylinder and excitation winding being spaced from said core to form a vacuum chamber therebetween, said vacuum chamber providing thermal insulation, said holding members extending through said vacuum chamber, said excitation winding having conductors of high field superconducting material and conductors of normal conducting material having good electrical conductivity properties at operating temperatures, the normal conducting conductors being arranged so that alternating currents which occur in said excitation winding during the operation of said turbogenerator occur only in said normal conducting conductors; and

coolant duct means extending substantially parallel to and being connected to said normal conducting conductors.

2. A turbogenerator as claimed in claim 1, wherein said excitation winding and said coolant duct means are combined into a single excitation winding coolant duct unit.

3. A turbogenerator as claimed in claim 1, wherein said carrier cylinder comprises non-magnetic steel insulated from said excitation winding.

4. A turbogenerator as claimed in claim 1, wherein said carrier cylinder comprises fiber-reinforced synthetic material.

5. A turbogenerator as claimed in claim 1, further comprising a damping cylinder of non-magnetic normal conducting material afiixed to said core and surrounding said carrier cylinder.

6. A turbogenerator as claimed in claim 1, further comprising axial mounting means mounting said carrier cylinder on said core, said axial mounting means comprising a support member of hollow substantially cylindrical configuration of poor thermal conductivity having one base area afiixed to said carrier cylinder in the area of one base of said carrier cylinder and another base area affixed to said core.

7. A turbogenerator as claimed in claim 1, wherein said core has plurality of spaced planar surfaces formed on its peripheral surface in diiferent areas, and further comprising torque transfer means affixing said carrier cylinder to said core and transferring torque from said core to said carrier cylinder, said torque transfer means comprising support strips of poor thermal conductivity extending substantially parallel to the planar surfaces formed on said core and each having one end affixed to said carrier cylinder and another end affixed to said core.

8. A turbogenerator as claimed in claim 2, wherein said excitation winding coolant duct unit comprises a tube of normal conducting material having a substantially rectangular cross-section formed by substantially planar inner surfaces, and a band of normal conducting material affixed to and extending along one of the inner surfaces of said tube and having a plurality of conductors of high field superconducting material embedded therein and extending therewith.

9. A turbogenerator as claimed in claim 2, wherein said excitation winding coolant duct unit comprises two tubes of normal conducting material each having a substantially rectangular cross-section, said tubes being spaced from each other by a small distance, and a band or normal conducting material positioned between and extending along said tubes and having a plurality of conductors of high field superconducting material embedded therein and extending therewith.

10. A turbogenerator 'as claimed in claim 2, wherein said excitation winding coolant duct unit comprises a tube of normal conducting material having a substantially rectangular cross-section having a plurality of conductors of high field superconducting material embedded therein and extending therewith.

11. A turbogenerator as claimed in claim 2, wherein said excitation winding coolant duct unit comprises a tube of electrical insulating material having a substantially rectangular cross-section formed by substantially planar inner surfaces, two bands of normal conducting material each on one of said inner surfaces opposite the other end extending therealong, and a third band of normal conducting material extending substantially radially to said core and between and substantially perpendicular to said two bands of normal conducting material, said third band of normal conducting material extending with said two bands of normal conducting material and forming therewith an I in cross-section thereby dividing said tube in half along its length to form two independent ducts, said third band having a plurality of conductors of high field superconducting material embedded therein and extending therewith.

12. A turbogenerator as claimed in claim 2, further comprising a rotor shaft extending from one end of said core and having an axis, coolant supply means for supplying coolant to said excitation winding coolant duct unit, said coolant supply means comprising a tubular supply duct coaxial with the axis of said rotor shaft extending in axial direction from one end of said rotor shaft into said core and through said core to said excitation winding coolant duct unit, coolant removal means for removing coolant from said excitation winding coolant duct unit, said coolant removal means comprises another tubular duct coaxially surrounding said supply duct and extending from said excitation winding coolant duct unit through said core to said rotor shaft and through said rotor shaft to said one end of said rotor shaft, and thermal insulating means around said coolant supply means and said coolant removal means for insulating said coolant supply means and said coolant removal means from each other, from said rotor shaft and from said core.

13. A turbogenerator as claimed in claim 6, wherein the support member of said axial mounting means is of hollow substantially frustoconical configuration.

14. A turbogenerator as claimed in claim 6, wherein the support member of said axial mounting means has a plurality of holes formed therethrough.

15. A turbogenerator as claimed in claim 7, wherein each of the support strips of said torque transfer means is aflixed to said core by fibers of material of poor thermal conductivity.

16.. A turbogenerator as claimed in claim 7, wherein each of the support strips of said torque transfer means has ribs formed therein.

17. A turbogenerator as claimed in claim 7, wherein each of the support strips of said torque transfer means has ribs formed therein and extending along its length.

18. A turbogenerator as claimed in claim 7, wherein said core has a plurality of spaced bores formed therein extending radially inwardly from its peripheral surface, and further comprising fastening means afiixing said carrier cylinder to said core, said fastening means comprising support rods of poor thermal conductivity housed in the bores formed in said core each having one end affixed to said carrier cylinder and another end aflixed to said core at the base of a corresponding one of said bores.

19. A turbogenerator as claimed in claim 8, wherein said conductors of high field superconducting material comprise superconducting wires parallel to and spaced from each other.

20. A turbogenerator as claimed in claim 10, wherein said tube has a plurality of substantially planar inner surfaces forming its rectangular cross-section and a plurality of substantially planar outer surfaces substantially parallel to said inner surfaces, and wherein said conductors of high field superconducting material comprise superconducting wires spaced from each other and spaced from each of the outer surfaces substantially parallel to the axis of said core by a distance greater than 16 five times the depth to which AC component s penetrate said tube of normal conducting material.

21. A turbogenerator as claimed in claim 12, wherein said thermal insulating means comprises a vacuum chamber.

22. A turbogenerator as claimed in claim 12, further comprising two thermally insulated normal conducting rings coaxially surrounding said rotor shaft at said one end thereof, each of said rings having a substantially cylindrical outer peripheral surface and a substantially cylindrical inner surface, a pair of normal conducting current leads each electrically contacting the peripheral surface of a corresponding one of said rings, a pair of conductors each comprising normal conducting material and high field superconducting material and each electrically contacting the inner surface of a corresponding one of said rings in radial alignment with the point of contact of the corresponding normal conducting current lead, a thermally insulated bore formed in said rotor shaft and extending to the tubular supply duct of said coolant supply means and a thermally insulated bore formed in said rotor shaft and extending to the other tubular duct of said coolant removal means, one of said pair of conductors extending through one of said bores and said tubular supply duct to said excitation winding coolant duct unit and the other of said pair of conductors extending through the other of said bores and said other tubular duct to said excitation winding coolant duct unit.

23. A turbogenerator as claimed in claim 20, wherein said distance is greater than 2.5 mm.

24. A turbogenerator as claimed in claim 22, wherein coolant from said coolant removal means cools said rings and parts of said pair of conductors.

References Cited UNITED STATES PATENTS 3,242,418 3/1966 Mela et al. 3l0-52 X 3,289,019 11/1966 Buchhold 3l052 3,368,087 2/1968 Madsen 310-52 X 3,405,290 10/1968 Halas 31010 3,443,134 5/1969 Dowsett et al 3l0--5'2 X DONOVAN F. DUGGAN, Primary Examiner US. 01. X.R. 310-86 

